Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle mounted on the tower, and a rotor coupled to the nacelle. The rotor typically includes a rotatable hub and a plurality of rotor blades coupled to and extending outwardly from the hub. The rotor blades capture kinetic energy of wind using known airfoil principles. More specifically, the rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to the gearbox, or if the gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Each of the rotor blades are generally mounted to hub via a pitch bearing that is configured to rotate an angle of each of the blades with respect to the wind. For example, the rotor blades may be pitched to feather or to power depending on the wind speed near the wind turbine. More specifically, as the wind speed increases from cut-in wind speed to rated speed, the rotor blades are typically pitched to power to maximize energy captured by the wind turbine. As the wind speed increases above rated wind speed, the rotor blades are typically pitched to feather, i.e. towards the incoming wind, via the pitch bearing such that the angle of attack decreases, forces decrease, and power is shed. For many wind turbines, the typical feather blade angle is from about 80 degrees to about 90 degrees.
The feather position for the rotor blades can lead to a very slow rotor idling, e.g. with one blade in front of the tower. In addition, the rotor may be locked with one rotor blade in front of the tower having a pitch angle around the feather position. Such situations can lead to vortex-induced tower vibrations due to interactions between the tower and the feathered rotor blade located in front of the tower.
In view of the aforementioned, the present disclosure provides a system and method for controlling the blade angle of the rotor blade in front of the tower based on tower vibration and/or rotor speed so as to reduce the danger of vortex-induced tower vibrations.